Respiratory apparatus

ABSTRACT

Respiratory apparatus comprising a ventilation mask ( 10 ) and means for supplying breathable gasses, under pressure, thereto and means for exhausting gases therefrom, is wherein the pressuring means is provided substantially at the inlet of the mask ( 10 ), thereby substantially reducing the length of the air supply hose to a ventilation mask ( 10 ), so that problems associated with high pressures and large volumes of dead space can be alleviated.

The present invention relates to respiratory, or ventilation, apparatuscomprising a face mask and means for supplying pressurised air thereto,as well as to valves useful in such devices.

Non-invasive, mask-type ventilators, which include a face mask,pressurised air supply and valve, are known. These ventilators sufferfrom various disadvantages, primary amongst which is inflation of theabdomen via the oesophagus. As the stomach becomes inflated, this pushesup the diaphragm which, in turn, reduces lung volume and, concomitantly,tidal volume (V_(t)).

In addition, the ventilators of the prior art are not only cumbersome,but substantially restrict movement of the patient, as the pressurisedair supply involves a length of tubing running from the mask to a fixedsource of air or other suitable, breathable gas supply. The mask andtubing arrangement also tends to be heavy and somewhat inflexible,thereby putting further strain on the patient.

The substantial length of the tubing also tends to add somewhatsubstantially to the dead space. In this context, the dead space is thatvolume of air involved in the overall tidal flow which never comes intocontact with gas exchange surfaces, in particular, the alveoli. When apatient is breathing normally, the dead space mainly comprises thetrachea, nose and pharynx which, together, form about 150 ml of a total600 ml tidal volume.

Using a mask of the prior art, the air supply tube may have a 10 mminternal radius and a length of 1800 mm, which provides an extra deadspace, in addition to the 150 ml naturally occurring, of about 558 ml,thereby virtually doubling the tidal volume, as well as at leastdoubling the pressure required to effect satisfactory ventilation. It issuch pressures which lead to problems with gas build up in the stomach.

One solution to the problem is to increase tidal flow and to createleaks in the mask to allow exhaust air, rich in carbon dioxide, toescape to help reduce the dead space problem. Another option is toprovide a valve in the tubing to allow exhaled air to escape at anearlier stage. Both of these options still require substantial pressureto achieve satisfactory ventilation.

To achieve exhaust of CO₂ in current masks, continuous positive flowand, therefore, pressure is required, even during exhalation of thepatient. The pressure required to achieve this flow is around 8 cm H₂Oor greater. This forms the basic expiratory pressure which the patientfaces at exhalation and which needs to be overcome in order for thepatient to exhale. This pressure increases the work of breathing anddistends lung volume, potentially beyond the need of the patient, whileat least the same amplitude (the difference between peak inspiratory andtrough expiratory pressures) is required to achieve adequate tidalvolume, so that 0-10 cm H₂O for a normal patient becomes 8-18 cm H₂O (ormore) for a patient using a face mask. The effects may be even moredeleterious, as tidal volume of 0-10 cm H₂O is greater than 8-18 cm H₂Odue to the lung pressure-volume curve.

One type of mask ventilator providing positive pressure ventilation, andwhich is non-invasive, is disclosed at page 609 of “Respiratory CareEquipment”, 2_(nd) edition, 1999. A valve therein relies on naturalexhalation, so that it is activated by expiration to cut off or reducethe supply of positive pressure, thereby enabling the patient to breatheout. In this type of ventilator, only one phase of the respiratorycycle, the inspiratory phase, is assisted and therefore active. This hasthe disadvantage that it is not possible to increase the respiratoryrate above 4-30 cycles per minute, as there is no option to do anythingother than rely on the natural expiration of the patient. As passiverecoil generally requires a minimum of one second, this means that suchventilators cannot work at more than 30 cpm. There is an exhaust valvein the power unit, so that dead space is still a problem, and there is asingle pressure chamber through which air from the blower passes, eitherto the patient during inhalation, or through an exhaust, duringexhalation in order to reduce or cut off supply.

Swiss Patent no. CH685678 discloses an inhaler comprising a base-shapedcontainer in which pressurised oxygen is stored. French PatentApplication no. FR2446115 discloses a resuscitator, which fits over themouth of the patient to supply air from a bulb, further comprising atongue depressor. Pressure, created by an hand-operated airbag or bulb,forces air into the mouth of the patient.

U.S. Pat. No. 3,216,413 discloses a hand-operated concentricbellows-type resuscitator apparatus for artificial respiration without ahose, wherein one bellows is situated within a second bellows, and thereis an arrangement of valves to enable assisted inhalation and exhalationof air from the patient's lungs at the appropriate pressures.

U.S. Pat. No. 3,939,830 discloses a manually operated resuscitator ordechoker for removing an obstruction from the throat of a patient. Inand out strokes of a piston are used to inflate and deflate the lungs ofthe patient.

U.S. Pat. application No. 2003/0111074 discloses a positive pressurehood comprising a power operated blower which forces air through afilter in order to generate a positive pressure within the hood. Aone-way purge valve exists for the exhaust of exhaled gases. Theapparatus is only suitable for maintaining a clean air supply, forinstance in a laboratory or other contaminated environment, inside thehood and, therefore, is not suitable for respirating a patient EuropeanPatent Application no. 0 352 938 discloses a powered respiratorcomprising a motor driven fan unit which draws air through an upstreamfilter unit, or alternatively, forces air through a downstream filterunit, for delivery to a face piece. The fan is triggered by a pressuresensor, which detects inhalation or exhalation by the patient leading toa corresponding assistance by the fan. Therefore, this device requiresthe patient to be breathing in the first place and cannot, therefore, beconsidered a respirator.

The object of the device disclosed in European Patent Application no. 0352 938 is to save battery life by only triggering the fan wheninspiration is required. Thi is achieved by matching fan output to theinhalation of the user. Furthermore, the apparatus comprises significantdead space of its own, as can be seen in FIG. 1, with the associatedproblems this entails, as discussed above.

Surprisingly, it has now been found that, by substantially reducing thelength of the air supply hose, problems associated with high pressurescan be alleviated.

Thus, in a first aspect, there is provided respiratory apparatuscomprising a ventilation mask and means for supplying breathable gasses,under pressure, thereto and means for exhausting gases therefrom,characterised in that the pressuring means is provided substantially atthe inlet of the mask.

By supplying the pressurising effect at the inlet of the mask, ratherthan at a distance through a tube, the creation of a substantial amountof dead space is avoided, and substantially lower pressures and flow areeffective to achieve ventilation, given that less CO₂ needs to beflushed out, as there is little or no tube. Indeed, it is now possibleto use sufficiently low pressures that portable, battery operateddevices can be employed-and worn-by-patients, thereby allowingsubstantially unfettered movement, where the patient is capable.

In order to provide the required pressure at the mask interface, asuitable fan pump may be provided. The fan may be driven directly by apower supply and motor co-located therewith. Alternatively, the powersupply, for example in the form of batteries, may be provided elsewhere,such as in a pocket. It is also feasible for the motor to be provided ata distance, and linked by a suitable gear link or train to the fan.

In general, it is preferred that a lightweight, motorised air pump beprovided, mounted directly on the mask, with a remote power supplyconnected, for example, by suitable cables, or other means. Suitablepumps are centrifugal impeller blowers, of the type illustrated atwww.rietschle.co.uk/principles/radial.asp, suitably miniaturised, orotherwise adapted, to provide a preferred maximum flow of 50 L/min. Thiscontrasts with the 180 L/min used in the art, and reflects the benefitsof the present invention, as well as enabling a portable power source tobe used.

It is preferred that the maximum inspiratory pressure output be in theregion of 25 cmH2O, with a range of 5-12 cmH₂O being preferablyemployed, in use. Again, this compares extremely favourably with thestandard 15-20 cmH₂O and up to 30-35 cmH₂O used in standard maskventilators. The pressures used in the present invention areconsiderably more effective than those used in the art, as dead spaceand tidal volume problems are minimised, and there is much betterresponse at lower pressures, as seen in pressure volume curve. It ispreferred that the pumps used in the present invention have a voltagerequirement of no more than 24V, preferably no more than 15V, with arange of 6-12V being preferred, although any pump or impeller capable ofproviding the requisite flow may be used.

The air supplied for breathing by the patient may simply be atmosphericair, in which case there is not generally any requirement for a supply,other than an atmospheric supply. However, where any other form ofbreathable gas is required or desired, then this may be supplied in anysuitable fashion to the pump or, if only required in less than 100%quantities, independently of the pump.

The exhaust means may comprise a simple valve in the mask which is notgenerally activated by the pressure generated by the pump, alone, but isonly activated by exhalation of the patient.

Whilst this embodiment provides many advantages over the prior art, itis generally preferred to enhance the respiratory apparatus of theinvention by further incorporation of a valve to regulate air, or gas,pressure supplied to the mask.

It is also preferred to employ both the inlet and exhaust ports of thepump when providing ventilation in association with such a valve.Particularly suitable pumps for use in this connection are lightweight,centrifugal pumps, such as illustrated above, which draw air in at, ornear, the rotational axis of the fan and generate an increased airpressure at the perimeter of the rotor, or impeller, which can beexpressed via a suitable port. In an advantageous embodiment, both theinlet and the outlet ports of a centrifugal fan are provided in the sameface of the pump. This has the advantage of facilitating interactionwith the valve.

It is a particular advantage of this aspect of the present inventionthat it is possible to fully control the I/E Ratio (the inspiratory toexpiratory time ratio), as there is no dependency on passive recoil ofthe lungs, so that both phases of the respiratory cycle may be fullycontrolled and active, allowing the I/E Ratio to be varied topractically any desired level.

Suitable valves of the present invention may comprise two body portionsseparated by a rotatable valve plate. A first body portion interactswith the ventilation mask, and may be secured thereto by any appropriatemeans, either fixedly or removably. Where the body portion is removable,attachment may be by any suitable means, such as interference fit, pushfit or snap fit, for example.

The first body portion preferably defines a mask access chamberconnecting both to the interior of the mask and the valve plate, and anexhaust chamber having an outlet to the atmosphere and connecting withthe valve plate, but not the ventilation mask. Communication between thetwo chambers is generally prevented by the valve plate.

The valve plate locates over the first valve body and has openings toprovide communication between the chambers of the first value body andthe second valve body portions. Movement of the plate, such as byrotation, serves to define how the chambers of each valve body portioncommunicate with the other. For ease, the openings in the valve plateare generally sectorial and identical in size, and it is preferred thatthe valve plate works in a back-forwards, or contra-rotatory, motion, inthis case allowing complete control of the I/E ratio to be achievedthrough control of the time spent in the different sections of thevalve. As such, it is also generally preferred that the valve sectionor, at least that part containing the valve plate, is circular, althoughit will be appreciated that the housing and walls surrounding the valvemay be any appropriate configuration, as desired, and may have anyappropriate configuration suitable to manual manipulation, for example.

It is preferred that the valve plate be mounted on a spindle or otheractuatable means suitable to effect movement to locate the apertures inthe plate in conjunction with the appropriate chambers in the valve bodyportions. The spindle may be actuatable by a second motor means, forexample. This second motor is preferably controlled and may beresponsive to the patient (in a triggered or synchronised mode) orexternal settings (in a controlled mode).

When responsive to the patient, exhalation may trigger the plate to moveto allow or encourage exhalation. Similarly with inhalation, as bothphases of the respiratory cycle may be fully and actively controlled.Suitable detector elements located in the mask can provide a signal toan effector associated with the motor.

Alternatively, the pump may be controlled independently of the patient'sbreathing, and set to a certain required pressure, for example. With thevalves of the invention, the speed and number of cycles can bedetermined and this can readily exceed 1000/minute cpm or even higher.

The second valve body portion comprises at least two chambers, one ofwhich is enclosed and corresponds to the pressurised air, or gas. Theother chamber serves as a conduit for exhaust air. Both chambers arelocated to communicate with the chamber in the first body portioncommunicating with the mask, depending on the positioning of the valveplate. Where it is desired that the patient should simply exhale, andnot be subject to any pressure, either positive or negative, then theexhaust chamber in the second valve body portion may be open to theatmosphere. This chamber, or a further chamber, may be connected to theinlet of the pump, in order to subject the patient to negative pressureto encourage exhalation, in which case it will be appreciated that thechamber will connect only with the inlet of the pump on the one hand andthe connecting chamber of the first body portion on the other hand, whenthe valve plate is in the correct configuration.

In a preferred embodiment, a valve of the invention has three possiblesettings, providing the patient with positive pressure, negativepressure or simply atmospheric pressure. In this embodiment, the secondbody portion of the valve will comprise at least three chambers. Afourth, null chamber, or simple land, may be provided opposite theatmospheric chamber, for example. Where a null chamber is provided, thismay be open, if desired.

It will be appreciated that, when the outlet of the pump is connected tothe connecting chamber in the first body portion of the valve, then theinlet of the pump will be connected to the chamber in the first bodyportion of the valve which connects and, therefore, is exhausted to theatmosphere. Likewise, when the inlet is connected to the connectingchamber, then the outlet will be connected and exhausted to theatmosphere.

The above pump embodiments are particularly preferred, and form aseparate aspect of the invention and, in particular, for use withrespiratory apparatus of the present invention, or any other respiratoryapparatus.

The ventilation mask is not critical to the present invention.Conventional masks may be used or adapted, and it is generally preferredthat they provide a substantially gas-tight linkage with the airways ofthe patient.

The present invention may also be applied to an apparatus where the maskportion is replaced by an endotracheal tube or means for connecting tosuch a tube.

Thus, in a further aspect, the present invention also provides arespiratory apparatus comprising a means for conducting breathablegasses directly to the trachea, via a tracheotomy or via a tube throughthe mouth to the trachea, and a means suitable for supplying thebreathable gasses, under pressure, thereto and means for exhaustinggases therefrom, characterised in that the pressuring means is providedsubstantially at the site of the tracheotomy or the patient's mouth.

The means for conducting breathable gasses directly to the trachea ispreferably an endotracheal tube with, optionally, a standard connectionfrom the endotracheal tube to the means suitable for supplying thebreathable gasses.

Alternatively, the means for conducting breathable gasses directly tothe trachea is preferably a connecting means for linking the apparatusin a substantially air-tight manner to an existing endotracheal tube.

The endotracheal tube may be connected to the rest of the device throughthe patient's mouth and tracheal opening, or, more preferably, through ahole or incision in the patient's throat, for instance a tracheotomy. Inthis instance, the pressuring means is provided substantially at theinlet of the tracheotomy.

Thus, this aspect of the present invention is preferably suitable foruse in conventional invasive positive pressure ventilation (PPV), forinstance on a patient with a tracheotomy. Thus, the apparatus is,preferably, an invasive respirator.

The apparatus may also be suitably adapted as described in the presentapplication with respect to the mask aspect of the invention. Inparticular, the apparatus may comprise a valve, preferably as describedherein.

The apparatus can, preferably, operate as either a positive pressureventilator or a high frequency oscillator.

There are several advantages to using this aspect of the invention, forinstance as an invasive respirator. A direct connection can be made fromthe apparatus to the endotracheal tube, thus minimising the tubingrequired. The advantage this gives is again a reduction in dead spaceduring ventilation (although there is already less dead space in PPVthan in mask ventilators) and, therefore, lower pressures are requiredto adequately ventilate patients. Again, this helps avoid the negativeside effects of high pressures. Furthermore, as the apparatus can bedirectly connected to the trachea, this can result in a significantdecrease in the dead space associated with the patient's trachea andmouth, for instance as much as 50%.

The endotracheal tube may also form part of the mask according to thepresent invention, such that the respiratory apparatus comprises both amask and an endotracheal tube.

The apparatus is easy to clean and sterilize, as it has few parts andlittle or not rubbing, thus reducing the risk of infection for thepatient. Furthermore, the apparatus is small, lightweight and this, withthe option of being battery operated, allows the invention to be used asa mobile respirator that also takes up far less space when used in theintensive care. Monitoring can be done as in conventional ventilators bysending the information in a wireless manner, such as Bluetooth orinfrared, for instance.

Most mobile transport ventilators are either fairly large batteryoperated devices requiring substantial amounts of battery power or mostcommonly (due to this reason) smaller pneumatic devices that requirecompressed air for them to work. (See chapter 17 Branson et al“Transport Ventilators” p527-565, Respiratory Care equipment).

Pressures suitable for generation by the apparatus of the presentinvention are generally low by comparison with the prior art, andsuitable pressures have been found, for the mask, to be typically be5-12 cmH₂O above ambient pressure and, as a maximum, 25cmH₂O during theinspiratory phase and from a maximum of −5cmH₂O, to below, at or aboveambient pressure during the expiratory phase.

In the case of the endotracheal apparatus the pressures generated can behigher and are typically from a maximum of 40 cmH₂O during theinspiratory phase and from a maximum of −15 cmH₂O, to below, at or aboveambient pressure during the expiratory phase.

These pressures are for guidelines only, and it will be appreciated thathigher pressures, as well as lower pressures, may be employed, but theserequire greater input of power, and may be associated with the problemsof the prior art.

The present invention further provides a method of ventilating apatient, comprising equipping the patient with the apparatus,particularly the mask, as defined above, and activating the pump.

Preferably, the apparatus comprises a supply of oxygen or breathablegasses, for instance in a pressurised vessel or tank, or via aconnection to a source of said gasses.

Preferably, an oxygen supplement is fed through a connection to theapparatus, preferably to the valve, in order to increase FiO₂ (Fractionof Inspired Oxygen) to above room air level.

Any condition treatable by conventional ventilation apparatus or masksmay be treated in accordance with the present invention, and may coverpatients with sleep apnoea and lung diseases to those on life support,as may be directed by a skilled physician. Therefore, also provided is amethod of ventilating a patient in need thereof, comprising the use ofan apparatus according to the present invention.

Preferably, the apparatus is a respirator or ventilator. It is alsopreferred that the apparatus according to present invention controls thebreathing rate of the patient, rather the apparatus being triggered bythe breathing of the patient. Preferably, therefore, according to thisembodiment of the present invention, inspiration and expiration are nottriggered by the patient of his or her breathing, but are controlled bya suitable control device, such a s life support machine, for instance.Accordingly, the present invention may be used on a patient that is notbreathing on his or her own.

In a further embodiment of the present invention, the apparatus may alsocomprise a filter for removing contaminants, for instance, from theinspired and/or expired air.

Preferably, the apparatus comprises means for reversibly securing theapparatus to the face or neck of the patient, as appropriate, therebyallowing the apparatus to be held in place and/or used in asubstantially hands-free manner, without the patient having to hold itin place. For instance, where the apparatus is a mask, it is preferredthat the means for reversibly securing the apparatus comprises at leastone or a plurality of straps or ties, suitable for the purpose, that maybe passed around the patient's head. The straps or ties are preferablyelastic.

Where the apparatus comprises an endotracheal tube, it is preferred thatthe straps or ties are suitable for passage around the patient's neck,for instance. -The apparatus may also comprise a series of flanges whichmay be used to secure the apparatus to the patient by means of bandages.

Preferably, the additional dead space added by the apparatus to thatnaturally occurring in the patient, is kept to an absolute minimum,preferably 200 ml or less, more preferably 100 ml or less, preferably 50ml or less, preferably 200 ml or less, preferably 25-50 ml, preferably10-20 ml, preferably 10-15 ml, preferably 5-10 ml more preferably 10 mland most preferably 5 ml or less.

The apparatus is also preferably biphasic such that it not only forcesair into the patient's lungs, but also actively expels the air from thelungs, rather than simply allowing the lungs to deflate naturally oftheir own accord, as is the case in many of the prior art devices. Bothphases may be triggered by the patients breathing, or may be under thecontrol of the apparatus, under the control of an onboard processor, orunder the control of a further control means, such as a life-supportmachine, for instance. This has the advantage of providing the user ordoctor with a greater degree of control with respect to theinspiration/expiration rate.

The invention will now be further illustrated with reference to theaccompanying drawings, in which:

FIG. 1 illustrates a mask and valve of the present invention where thevalve has three pressure settings;

FIG. 2 illustrates a valve of the present invention having two pressuresettings;

FIG. 3 illustrates a valve for use with the present invention; and

FIG. 4 illustrates an alternative embodiment of the valve of FIG. 1.

In FIG. 1, there is shown face mask (10) having processes (20) for theattachment of straps, or the like, to secure the mask (10) over themouth and nose of the patient (not shown).

Valve (30) is shown in three sections (40, 50, 60) and is locatable inaperture (25) of mask (10) via flange (65) of first body portion (40).Connecting chamber (70) provides an unobstructed passageway between theinside of mask (10) and valve plate (50). Chamber (75) is sealed by land(80), and does not provide gaseous communication with the inside of mask(10). Exhaust slot (85) provides communication with the externalatmosphere.

Valve plate (50) is provided with spindle (90), which locates incorresponding recess (95) in first valve body portion (40). Spindle (90)is suitably equipped with external drive means (not shown) to effectrotation.

Apertures (100, 105) control communication between first valve bodyportion (40) and second valve body portion (60). The periphery of thevalve plate (50) locates on internal flange (110) in valve body portion(40), thereby providing a gas-tight seal, or substantially gas-tightseal. It will be appreciated that with the general volume of air flow,it is not necessarily important that the seal be especially gas-tight,provided that any gas getting past the seal does not substantiallyinterfere with the desired ventilation effect.

Second valve body portion (60) is equipped with four chambers (120, 130,140, 150) equipped with slots (123, 126, 133, 136, 145, 155). Impellerend plate (160) is shown, with negative pressure port or inlet (165) andpositive pressure port, or outlet (170). The rest of the impeller is notshown. Positive port (170) corresponds with chamber (120) of secondvalve body portion (60), while negative port (165) corresponds withchamber (130). When aperture (100) is located over aperture (133), thenaperture (105) will be located over aperture (123). In thisconfiguration, negative port (165) communicates via aperture (133) andaperture (100) with communicating chamber (70) to reduce the pressure inmask (10). At the same time, positive pressure port (170) acts viaapertures (123, 105) to exhaust via slot (85) in dead end chamber (75).

Rotating the valve plate (50) to engage aperture (100) with aperture(136) places aperture (105) in conjunction with aperture (126), so thatthe reverse effect is achieved. Namely, negative port (165) communicatesvia apertures (136) and (100) with null chamber (75) to draw in airthrough slot (85) while positive pressure port (170) communicates viaapertures (126) and (105) with communicating chamber (70) to raise thepressure in the mask (10). It will be appreciated that the same effectwill be achieved if aperture (105) corresponds to aperture (136) ratherthan aperture (126), and that the one configuration of the two possibleis described for purposes of simplicity. Similar considerations apply toany other configuration where a plurality of equivalent possibilitiesexists.

In a third configuration, apertures (105) and (100) interact withapertures (145) and (155), respectively. In this configuration, as withall other configurations of this embodiment, neither chamber (150) noropen chamber (140) corresponds to any port on the impeller. Thus, inthis configuration, the effect is to provide a direct atmospheric linkto the mask via connecting chamber (70) and apertures (100) and (145),the lack of wall in chamber (140) providing immediate access to theatmosphere.

In FIG. 2, valve (30′) is shown, consisting of first valve body portion(40′), valve plate (50′) and second valve body portion (60′). In thisembodiment, the numerals have the same meanings as in FIG. 1.

An alternative version of the first valve body portion (40′) is shown,in which the chamber (75) is not hollowed in any fashion, thereby simplyproviding an aperture (85) communicating with the atmosphere, in thechamber.

In second valve body portion (60′), chambers (140) and (150) are notpresent, so that only positive pressure chamber (120) and negativepressure chamber (130) are provided. In this configuration, negativepressure is provided to the ventilation mask when aperture (100)corresponds with aperture (133) and aperture (105) corresponds withaperture (123). Positive pressure is provided when aperture (100)corresponds with aperture (126) and aperture (105) of the valve plate(50′) corresponds with aperture (136).

In FIG. 3 valve (30″) is for use with a blower where only the positivepressure outlet engages with chamber (120) of valve bodyportion (60″).Chamber (130) is open to the atmosphere. There is no slot (85) in valvebody portion (40′). Instead, chamber (72) connects directly to opening(123) in valve body portion (60′) when opening (105) in valve face plate(50′) is appropriately located.

When opening (105) corresponds with opening (133), then positivepressure is fed into the mask via chamber (70), while chamber (72) isclosed by valve face plate (50′).

Valve face plate (50″) may also occupy a central position where slot(105) corresponds to neither opening (123) nor opening (133), so thatair may neither pass in nor out of the mask in this configuration. Thismay be appropriate between inhalation and exhalation, for example.

As with FIGS. 1 and 2, recessed portion (180) locates within and abutsagainst lip (185) on valve body section (40′).

FIG. 4 depicts a valve embodiment similar to that of FIG. 1, andfunctions in a similar manner. In this embodiment, valve body portion(40′″) is lacking land portion (72) such that, when any of openings(136), (155) and (123) is exposed by either of openings (100) and (105),then direct contact with the ambient atmosphere is made.

Chamber (70) in body portion (40′″) takes the form of a lumen in malemember (75) which docks with female member (78) in the mask (10).Openings (126), (145) and (133) communicate with lumen (70) when exposedthereto by either of openings (100) and (105) via chamber (72) recessedbeneath flange (110), providing positive, negative or atmosphericpressure, as desired.

It will be appreciated that variations are possible in the embodimentsof the above Figures and that it is possible to vary the amount ofpressure in the mask by varying the degree to which any particularaperture is open. For example, it may be desirable to continue toprovide a lesser positive pressure during exhalation rather thanatmospheric or negative pressure. Where desired, this may be effectedeither by lowering pressure in the blower, or preferably by controllingpressure through the I/E Ratio, thereby maintaining an overall positivepressure in the mask, even where the disc is allowing atmospheric ornegative pressure into the mask. Although it is possible to vary thespeed of the impeller, it is generally preferred to keep this at aconstant rate, except when the ventilation device is switched off, inorder to conserve energy and provide the most rapid possible reactiontime.

1. Respiratory apparatus comprising a ventilation mask and means forsupplying breathable gasses, under pressure, thereto and means forexhausting gases therefrom, characterised in that the pressuring meansis provided substantially at the inlet of the mask.
 2. Respiratoryapparatus comprising a means for conducting breathable gasses directlyto the trachea of a patient, via a tracheotomy or via a tube through themouth to the trachea, and a means suitable for supplying the breathablegasses, under pressure, thereto and means for exhausting gasestherefrom, characterised in that the pressuring means is so located asto impart pressure to said gasses immediately adjacent the site of thetracheotomy or the patient's mouth.
 3. Apparatus according to claim 1,further comprising a means for conducting breathable gasses directly tothe trachea, via a tracheotomy or via a tube through the mouth to thetrachea.
 4. Apparatus according to claim 1, wherein a motor for thepressuring means is co-located therewith.
 5. Apparatus according toclaim 1, where the power supply is portable.
 6. Apparatus according toclaim 5, where the power supply is in the form of batteries. 7.Apparatus according to claim 1 wherein the pressuring means is acentrifugal impeller blower.
 8. Apparatus according to claim 1, whereinboth the inlet and exhaust ports of the pressuring means arecommunicable with the mask, in use.
 9. Apparatus according to claim 8,wherein the inlet and the outlet ports of a centrifugal fan are providedin the same face of the pump
 10. Apparatus according to claim 1, furtherincorporating a valve to regulate air, or gas, pressure in theapparatus.
 11. Apparatus according to claim 10, wherein the valveregulates air, or gas, pressure in a mask.
 12. Apparatus according toclaim 11, wherein the valve comprises two body portions separated by arotatable valve plate the first body portion interacting with theventilation mask and defining a mask access chamber connecting both tothe interior of the mask and the valve plate, and an exhaust chamberhaving an outlet to the atmosphere and connecting with the valve plate,but not the ventilation mask; the valve plate locating over the firstvalve body portion and having openings to provide communication betweenchambers of the first valve body portion and the second valve bodyportion; the second valve body portion comprising at least two chambers,one of which is enclosed and corresponds to the pressurised air, or gas,and the other serving as a conduit for exhaust air, both chambers beinglocated so as to communicate with the chamber in the first body portioncommunicating with the mask, as determined by positioning of the valveplate.
 13. Apparatus according to claim 12, wherein the valve has threepossible settings to provide the patient with positive pressure,negative pressure or atmospheric pressure, and wherein the second bodyportion of the valve comprises at least three chambers, an optional nullchamber, or land, being provided opposite the atmospheric chamber, andwherein the atmospheric chamber exhausts directly to the atmosphere. 14.Apparatus according to claim 10, wherein the inspiratory to expiratorytime ratio is under the control of the apparatus.
 15. Apparatusaccording to claim 10, wherein the apparatus has the ability to operateat high frequency, up to 1000/minute cpm, or greater.
 16. Apparatusaccording to claim 1 which is a respirator or ventilator.
 17. Apparatusaccording to claim 1, wherein the pressure generated by the apparatus isfrom a maximum of 25 cmH₂O during the inspiratory phase and from amaximum of −5 cmH₂O, to below, at or above ambient pressure during theexpiratory phase.
 18. Apparatus according to claim 17, wherein thepressure generated by the apparatus is 5-12 cm H₂O above ambientpressure.
 19. Apparatus according to claim 1, wherein the apparatuscontrols the breathing rate of the patient.
 20. Apparatus according toclaim 2, wherein the means for conducting breathable gasses directly tothe trachea is an endotracheal tube with, optionally, a standardconnection from the endotracheal tube to the means suitable forsupplying the breathable gasses.
 21. Apparatus according to claim 2,wherein the means for conducting breathable gasses directly to thetrachea is a connecting means for linking the apparatus in asubstantially air-tight manner to an existing endotracheal tube. 22.Apparatus according to claim 2, wherein the endotracheal tube isconnected to the rest of the device through a tracheotomy.
 23. Apparatusaccording to claim 2, wherein apparatus is an invasive respirator. 24.Apparatus according to claim 2, wherein the pressure generated by theapparatus is from a maximum of 40 cmH₂O during the inspiratory phase andfrom a maximum of −15 cmH₂O, to below, at or above ambient pressureduring the expiratory phase.
 25. Apparatus according to claim 1, whereinthe apparatus comprises a filter.
 26. Apparatus according to claim 1,wherein the apparatus comprises a means for reversibly securing theapparatus to the face or neck of the patient.
 27. Apparatus according toclaim 1, wherein the apparatus comprises a supply or feed of oxygen orbreathable gasses.
 28. Apparatus according to claim 1, wherein theapparatus comprises a means for reversibly securing the apparatus to theface or neck of the patient, thereby allowing the apparatus to be heldin place and/or used in a substantially hands-free manner.
 29. Apparatusaccording to claim 1, wherein the additional dead space added by theapparatus is 25-50 ml, or less.
 30. Apparatus according to claim 29,wherein the additional dead space is 5-10 ml, or less.
 31. Apparatusaccording to claim 1, wherein the apparatus is biphasic.
 32. A method ofventilating a patient, comprising equipping the patient with apparatusof claim 1, and activating the pressuring means.
 33. A method ofventilating a patient in need thereof, comprising the use of anapparatus of claim
 1. 34. A valve as defined in claim
 11. 35. Apparatusaccording to claim 2, wherein a motor for the pressuring means isco-located therewith.
 36. Apparatus according to claim 2, where thepower supply is portable.
 37. A method of ventilating a patient,comprising equipping the patient with the apparatus of claim 2, andactivating the pressuring means.
 38. A method of ventilating a patientin need thereof, comprising the use of the apparatus of claim 2.